This invention relates to extended rubber compositions.
Oil extended rubbers are an important product of the rubber industry. Aromatic or naphthenic oils are generally used and as much as 60 parts by weight of oil per 100 parts by weight of rubber may be incorporated in these extended rubbers. Principally these extender oils serve as process aids and as a means to reduce the cost per unit of manufactured product.
However, some rubbers do not accept oil very well and suffer property degradation which makes them less desirable in certain applications. Also in many instances it is necessary to balance the competing properties so that a polymer, produced under conditions designed to give it sufficient strength, may be difficult to fabricate due to low melt flow.
Recently there had been developed a new class of rubbers known as plastomers or thermoplastic elastomers. These materials are thermoplastic in the same sense as resinous thermoplastic materials in that they can be remelted and molded; however, they have rubbery properties without the use of a curing agent. Basically, these rubbers comprise an internal rubbery polymer block with terminal blocks of essentially polymerized monovinyl-substituted aromatic compound. The rubbery block can be a diene homopolymer or a predominantly diene copolymer, either random or block.